Method and device for electronically correcting the color value in film scanners

ABSTRACT

A method for digitizing images stored on film material has, after the image conversion by means of a digitizing device ( 3 ) firstly an electronic color value correction independent of user inputs. A user-controllable correction and manipulation of the electronically stored information is subsequently carried out only after the electronic color value correction, which is effected in a manner dependent on properties of the digitizing device ( 3 ) and on film material properties. The electronic color value correction depends on parameters which can be adapted to varying properties of the digitizing device ( 3 ). A film scanner adapted to this method has a digitizing device ( 3 ) and also a device for controllable correction ( 5 ) of the converted image data. A device of discrete construction for electronic color value correction ( 5 ) is connected between the digitizing device ( 3 ) and the device for controllable correction ( 4 ). An interface ( 6 ) for reading in and reading out electronically stored correction data is connected to the device for electronic color value correction ( 5 ).

[0001] The invention relates to a method for digitizing images stored onfilm material, an image being converted into electronically storedinformation by means of a digitizing device and a user-controllablecorrection of the electronically stored information subsequently beingeffected, it also being possible to carry out an electronic color valuecorrection.

[0002] The continuously increasing computing power and storage capacityof electronic data processing systems enables not only individual imagesbut whole films to be digitized in virtually completely automatedfashion.

[0003] It is thus possible in the meantime for image and film documentsstored on film material to a large extent to be digitally conditionedand stored. Depending on the quality and storage conditions of theexposed film material, chemical processes may attack or even destroy thefilm material. By contrast, the digital image information can be storedand duplicated virtually without any losses over long periods of time.

[0004] Computer-aided or wholly computer-generated alterations of theimage information are being carried out to an increasing extent in filmproductions for television and cinema. In complex cinema productions,whole film sequences or even the entire film are processed subsequently.The alterations that are possible in this case range from slightlycorrective color or brightness changes through to the addition of new ordeletion of undesired image parts.

[0005] Recording techniques which enable the background or individualimage parts to be masked out in a simple manner have been developed.Thus, by way of example, the actors act in front of a homogeneously bluebackground, the “blue box”, during film recordings. In the course ofelectronic image processing, the blue background can then be replaced byan arbitrary other, possibly wholly computer-generated background.

[0006] Principally complex image manipulations of relatively long filmsequences require a high outlay on computing power and storage capacityand also processing time. In the case of film productions that are to bepost-processed in complex fashion, significantly more time and labor andresultant costs then have to be used for the post-processing of thedigitized images than for the actual film recordings. There are only asmall number of companies which specialize in this and are suitable dueto their size and technical equipment for the electronic post-processingof an extensive film project.

[0007] The film recordings are digitized by film scanners. For thispurpose, each individual image of a film is projected onto alight-sensitive electronic image converter, usually a CCD camera, by animaging unit. The projection of the individual image is then scanned byCCDs arranged in point, line or matrix form and is converted intoelectronic image information. In this case, each measured pixel isuniquely described by coordinates in a color system, usually the YcrCbsystem. The number of pixels that can be measured electronically perindividual image and also the accuracy with which the coordinates in thecolor system are defined substantially determine the quality of thedigitized image information. The technical possibilities permithigh-resolution digitizing of a film at a speed which correspondsapproximately to the playback of the film.

[0008] The digitized image information can be uniformly corrected andmanipulated for in each case individual images or a whole imagesequence. Correction of the electronic image data is regularly necessaryon account of the manufacturing tolerances of the optical and electroniccomponents of the film scanner. Depending on the film material used, thedigitized image information prior to correction would have significantdifferences in hue and saturation since the often broadband colorsensitivity of the film material usually deviates from the colorsensitivities—defined by filter systems—of the digitizing device of thefilm scanner. These in part clearly perceptible differences have to becorrected in the context of subsequent image processing. Thesecorrections are important in particular if digitized image sequences areto be combined with one another on different film scanners withdifferent color sensitivities.

[0009] Special film sequences that are standardized with a high outlayare used for determining the apparatus-specific correction data. In thiscase, the individual images have known, precisely defined color andbrightness values, so that the best possible correction of the measureddigitized image information can be determined.

[0010] The purpose of digitizing image sequences is always, exceptperhaps for archiving purposes, to effect more or less clearly visibleimage manipulation. The image data present electronically can be alteredas desired in this case. The retouching of individual image areas or themanipulation of the entire image content also corresponds essentiallyonly to changing the brightness and color value of a correspondingnumber of pixels.

[0011] The correction and also the deliberate image manipulation isaccordingly effected by the controlled changing of the pixelinformation, which usually comprises complex calculations requiring ahigh outlay, however.

[0012] The high resolution and digitizing speed requires acorrespondingly powerful hardware which can calculate, manipulate andstore the large data streams obtained in real time. Therefore, not justfor cost reasons, individual corrections and the deliberate imagemanipulation dependent on user inputs are combined both in thecalculation algorithms and by the circuitry arrangement of individualelectronic assemblies. Therefore, a single albeit complex calculation iscarried out for each pixel, which calculation is used to carry out boththe film-scanner-specific corrections and the diverse user-dependentimage manipulations. Algorithms such as matrix correction or 6-sectorcolor correction have proved to be advantageous in this case.

[0013] A complete separation of the correction calculation from theimage manipulation dependent on user inputs is possible only withdifficulty at the present time without the additional implementation ofcomputation steps near to the hardware. This is due to the position ofthe different color correction elements with respect to one another andthe thus incommensurately high computation complexity for a mutuallyindependent correction of the film scanner properties and theuser-dependent image manipulation. Thus, the calculations to be carriedout for each pixel are in part so complex that calculation steps arereplaced by references to values calculated in advance. In the case ofcomputation methods of this type, it is no longer possible to calculateback to individual starting parameters owing to the nonfunctionalrelationship. Accordingly, the correction with regard to properties ofthe film scanner is always also effected in a manner dependent on theuser inputs prescribed for the later image manipulation. Correctioncalculations given otherwise identical user stipulations also lead todeviating end results of the digitized and corrected image sequencesowing to varying physical properties of the digitizing device ofdifferent film scanners. A film sequence shown contiguously thereforealways has to be digitized on the same film scanner in order to enableidentical results of the digitized image information.

[0014] It is precisely in the case of relatively large projects, inwhich splitting between a plurality of film scanners or even a pluralityof production sites would be practical, that the restriction to a singlefilm scanner leads at least to unnecessarily long project executiontimes and cost risks. Any apparatus defect then inevitably leads to longdelays and in the worst case necessitates complete reprocessing of thefilm material.

[0015] Accordingly, it is an object of the invention to enable anindependent correction of the digitized image information with regard tothe apparatus-specific properties of the film scanner respectively used.An adaptation of the correction parameters to different film materialsshould likewise be able to be carried out independently of userspecifications.

[0016] This object is achieved according to the invention by virtue ofthe fact that an electronic color value correction independent of userinputs is carried out after the image conversion by means of adigitizing device and before the user-controllable correction.

[0017] The subsequent processing of the digitized image information isthereby subdivided into two method steps that proceed separately fromone another. In this case, the electronic color value correction carriedout first is completely independent of user inputs, so that the latterhave no influence on the correction calculations carried out directlyafter the electronic image conversion. Unambiguous separation intouser-independent and user-dependent method steps is thereby possible.

[0018] It is preferably provided that the electronic color valuecorrection is effected in a manner dependent on properties of thedigitizing device and on film material properties.

[0019] Unavoidable deviations of individual optical or electroniccomponents are a significant cause of varying measurement results indifferent film scanners. Production-dictated tolerances of the opticalcomponents and of the electronic digitizing unit have the effect, forexample, of reducing the resolution of the film scanner within specificregions of the color space. The electronic color value correctioncarried out directly after the digitization takes account of suchdeterminable properties of the film scanner. The correction calculationcan be calibrated by evaluation of individual images with preciselydefined color value information. This calibration can be carried out ineach case with the desired film material, with the result thatindividual adaptation even to different film material properties ispossible. Since the electronic color value correction carried out firstdepends only on the film scanner and the film material used, the sameimage sequence, in the event of digitization on different film scannerscalibrated in this way, leads to digitized image information that isidentical to the greatest possible extent. The electronic conditioningof film sequences can therefore be distributed as desired betweendifferent film scanners or even different work sites.

[0020] According to one refinement of the concept of the invention, itis provided that the electronic color value correction depends onparameters which can be adapted to varying properties of the digitizingdevice.

[0021] Properties that vary with time, for example of the light sourceused or of individual optical components, can appreciably alter theproperties of the film scanner. The individual components of the filmscanner are deliberately optimized for a best possible temporalstability. Thus, by way of example, the light source used to illuminatethe individual images must have a constant light emission over thelongest possible periods of time in order to avoid brightness and colorchanges brought about thereby within a progressively recorded imagesequence. Unavoidable alterations in the properties of the film scannernevertheless occur. These alterations can be minimized, for example byregular maintenance of the film scanner, but not completely prevented.The resulting deviations of the digitized image information can beacquired, however, and taken into account in the context of theelectronic color value correction. In this way, a film scannerdigitizing property that remains constant over a long period of time canbe ensured by means of regular recalibration of the film scanner.

[0022] It is provided that the user inputs for correction of theelectronically stored image information can be acquired and stored as aset of parameters and the parameters can be read in and out via aninterface.

[0023] The knowledge of these parameters can be used to simplify themaintenance of the film scanners by means of additional information. Itis also possible, by altering these parameters in a targeted manner, tooptimally adapt the correction of the digitized image information tovarying properties of the film material used. It is thus conceivable touse individual correction parameters to take account directly ofspecific properties of the film material such as, for example, the colorsensitivity of the film material used.

[0024] The invention also relates to an apparatus for carrying out themethod according to the invention having a digitizing device and acontrollable device for correcting the electronically storedinformation, wherein the apparatus has a device of discrete constructionfor electronic color value correction and the device for electroniccolor value correction is connected between the digitizing device andthe device for controllable correction of the electronically storedinformation.

[0025] In the method according to the invention, the electronic imageprocessing was subdivided into two method steps carried outindependently of one another. The calculations respectively requiredwould therefore have to be processed one after the other. For thispurpose, the electronic assemblies used would have to enable allconceivable image manipulations and could not be adapted to respectivespecific requirements. By contrast, a device of discrete constructionfor electronic color value correction can be optimized for this task.

[0026] It is advantageously provided that the device for electroniccolor value correction has an interface for reading in and reading outelectronically stored correction data.

[0027] In this way, it is possible to carry out the maintenance andcalibration of the film scanner completely independently of controldevices and settings selected by the user.

[0028] According to one refinement of the concept of the invention, itis provided that the apparatus has an interface for reading in andreading out electronically stored correction data. In addition to theapparatus-specific or film-material-dependent correction parameters, theimage processing parameters respectively selected by the user can alsobe interchanged via a generally utilizable interface. The film scannercurrently being used can thus be changed at any point in time whilstmaintaining all the parameters relevant to the image processing. Givenknowledge of all relevant parameters, even complex processing operationscan be documented and repeated reproducibly.

[0029] An exemplary embodiment of the invention is explained in moredetail below in the drawing.

[0030] The film scanner illustrated in the drawing has a light source 1,past which the film material 2 is moved. The imaging of an individualimage of the film 2 which is projected by the light source 1 isconverted into electronic image information by a digitizing device 3.The digitizing device 3 usually comprises a combination of opticallenses and filters and also a CCD chip arranged in line form or matrixform.

[0031] The image information present in electronic form after the imageconversion can be manipulated as desired by means of a device forcontrollable correction 4 before the image data are stored on suitablestorage media. The device for controllable correction 4 of the digitizedimage information usually comprises a large number of interconnectedprocessors and memory modules.

[0032] A device for electronic color value correction 5 is connectedbetween the digitizing device 3 and the device for controllablecorrection 4. The device for electronic color value correction 5 is ofcompletely discrete construction and independent of the device forcontrollable correction 4, which can be influenced by the user. Thecorrection calculations carried out in the device for electronic colorvalue correction 5 are dependent only on properties of the digitizingdevice 3 and of the film material 2 used. Only after the electroniccolor value correction has been carried out are the image data alteredand manipulated by means of the device for controllable correction 4 ina manner dependent on user stipulations.

[0033] The device for electronic color value correction 5 has aninterface 6 for reading in and reading out the correction data; saidinterface 6 may comprise for example a floppy disk or CD drive which canbe operated with the aid of a screen and a keyboard.

1. A method for digitizing images stored on film material, an imagebeing converted into electronically stored information by means of adigitizing device and a user-controllable correction of theelectronically stored information subsequently being effected, it alsobeing possible to carry out an electronic color value correction,wherein an electronic color value correction independent of user inputsis carried out after the image conversion by means of a digitizingdevice (3) and before the user-controllable correction.
 2. The method asclaimed in claim 1, wherein the electronic color value correction iseffected in a manner dependent on properties of the digitizing device(3) and on film material properties.
 3. The method as claimed in claim2, wherein the electronic color value correction depends on parameterswhich can be adapted to varying properties of the digitizing device (3).4. The method as claimed in claim 1, wherein the user inputs forcorrection of the electronically stored image information can beacquired and stored as a set of parameters and the parameters can beread in and out via an interface (6).
 5. An apparatus for carrying outthe method as claimed in claim 1 having a digitizing device (3) and acontrollable device (4) for correcting the electronically storedinformation, wherein the apparatus has a device of discrete constructionfor electronic color value correction (5) and the device for electroniccolor value correction (5) is connected between the digitizing device(3) and the device for controllable correction (4) of the electronicallystored information.
 6. The apparatus as claimed in claim 5, wherein thedevice for electronic color value correction (5) has an interface (6)for reading in and reading out electronically stored correction data. 7.The apparatus as claimed in claim 5, wherein the apparatus has aninterface for reading in and reading out electronically storedcorrection data.